Abstract

The fundamental goal of the log-based fault-tolerant scheme is to bring the system into a consistent global state without any orphan inconsistence. However, the existing Alvisi’s No-Orphans Consistency Condition is only sufficient on condition that the set of local checkpoints of failure processes keep consistent always. Independent of the specific log-based checkpointing and rollback-recovery fault tolerant scheme, an extended orphan-free consistency condition is derived based on PWD assumption in this paper. The definitions of the orphan inconsistence among the process state and the nondeterministic event during a rollback recovery were extended. Finally the essential requirement for message logs was specified to eliminate the possible orphan inconsistence among the process state during a rollback recovery. By contrast, the proposal is a practical and efficient constraint for the orphan-free recovery.

Distributed computing is asynchronous (Elnozahy, Alvisi, Wang, & Johnson, 2002). That means there are no bound on the relative speeds of processes and no global time source. The computation of the process is assumed to follow Piece-Wise Deterministic (PWD) model (Elnozahy, Alvisi, Wang, & Johnson, 2002; Alvisi & Marzullo, 1998; Park, Woo, & Yeom, 2002; Park, Woo, & Yeom, 2003). In other words, the process execution is a sequence of state intervals, each started by a nondeterministic event (Li & Wang, 2005). These experienced events among the process follow the irreflexive partial order, which can be denoted by happened-before relation for representing potential causality (Elnozahy, Alvisi, Wang, & Johnson, 2002).